The invention is based on a circuit arrangement for an optoelectronic contamination sensor for detecting foreign bodies on a transparent element
More particularly, it relates to a circuit arrangement for an optoelectronic contamination sensor for detecting foreign bodies on a transparent element, which has a dynamically driven reflection light barrier whose receiver is fed by a supply voltage via a working resistor. It is known that dust, dirt, rain or snow adversely affect the light transmission on windscreens or headlamp lenses of a motor vehicle. In order to eliminate the contamination, the window or lens is to be automatically cleaned. The cleaning of the window or lens is triggered by an optoelectronic contamination sensor which is insensitive to extraneous light which originates from light in the surroundings or the oncoming light of other headlamps or the vehicle's own headlamps.
German Offenlegungsschrift 36 19 208 discloses a device which detects a wet or dry contamination on the surface of a headlamp lens and, in the event of contamination, activates a cleaning system. In this device, an optical transmitter and receiver are arranged on the inside of the lens. The radiation emitted by the optical transmitter is reflected by contamination particles on the lens. The reflected radiation is largely picked up by the receiver and fed to an evaluation circuit.
It was shown in practice that the sensor signal was temporarily disturbed in particular by the reflection of the vehicle's own headlamp light such that, despite increasing contamination of the lens, the sensor signal no longer reached the trigger threshold for the switching on of the cleaning system. The circuit arrangement of the contamination sensor was then incapable of functioning.
The same problem occurred when there was a very large light incidence from oncoming vehicles, which is very troublesome in particular during night driving.